Numerous automatic welding apparatuses for piping have been introduced for the automatic circumferential multilayer welding of butted fixed pipings. The automatic welding apparatus refers to an apparatus including a welding head, a welding power source, a control unit, a coolant pump and so on, among which a torch body, and a unit including an electrode attached to the torch and a gas supply mechanism that supplies a shield gas around the electrode etc., will be hereinafter referred to as a welding torch, and such a welding torch, and a unit including members that supply the welding torch with power, a shield gas and a welding wire, and a coolant that cools the welding torch, will be hereinafter referred to as a welding head.
Referring to an automatic TIG (Tungsten Inert Gas) welding apparatus for piping in particular, which employs the TIG welding method, the welding head is clamped to the fixed piping, and a main body 1 of the welding torch is rotated around the outer circumference of the piping with the welding wire inserted into the welding section, so as to automatically perform the multilayer welding of the circumference of a butted portion of two tubes.
A furnace wall of a boiler is, as shown in FIG. 28, constituted of a plurality of pipings 28 aligned in a plane and connected to one another via a membrane bar 29, and includes butt-welded portions between the piping 28 and another piping 28. At the butt-welded portion of the two pipings 28 and 28, the butted portion 32 of the pipings 28 and 28 is beveled so that a welding bead is provided thereon, and the membrane bar 29 is not attached to the region close to the welding section for ease of the welding operation and hence a space is secured around the pipings 28 and 28.
On this boiler furnace wall, a spacing between the pipings 28 and 28 disposed parallel to each other is as narrow as approximately 17 mm, and this is where the butt-welding section is located. The main body 1 of the welding torch mounted on the welding head used for various conventional piping welding apparatuses is unable to pass through such a narrow working space. Accordingly, an ultra-flat welding torch has been proposed, in Japanese Published Unexamined Patent Application No. H09-271939 and Japanese Published Unexamined Patent Application No. H10-193103.